1. Field of the Invention
The present invention relates to an eddy current flaw detection system and an eddy current flaw detection method for scanning an eddy current flaw detection probe on an inspection surface.
2. Description of the Related Art
An eddy current flaw detection method is an inspection method of causing an alternating magnetic field generated by an exciting coil to induce eddy currents in a surface layer portion of a conductive object to be inspected and detecting a disturbance in eddy currents due to a flaw or crack as a change (change in output voltage) in impedance of a detecting or sensing coil, thereby determining the presence or absence of the flaw.
There has recently been proposed an eddy current flaw detection system using an eddy current flaw detection probe (hereinafter called a “multi-coil probe”) having a plurality of coils arranged on a substrate for the purpose of speeding up inspections (refer to, for example, JP-2008-8806-A (refer to FIGS. 14 and 15, etc.)). In the eddy current flaw detection system described in JP-2008-8806-A, a plurality of coils arranged in a direction orthogonal to a scanning direction of a multi-coil probe are sequentially switched to exciting and detecting coils while the multi-coil probe is being scanned on an inspection surface. That is, the multi-coil probe has a plurality of combinations (channels) of the exciting and detecting coils. Thus, for example, as compared with a case in which an eddy current flaw detection probe having only a single combination of exciting and detecting coils is used, a wide range of scanning is enabled and the shortening of an inspection time is made possible. Further, since the substrate of the multi-coil probe has flexibility (ductility), the multi-coil probe is capable of following the shape of the inspection surface.
In the above-described eddy current flaw detection system, each scan position of the probe is recorded and a result of detection of each channel (output voltage of detecting coil) is recorded. When a flat inspection surface is flaw-detected, for example, a scan area is displayed by a two-dimensional coordinate system in which each scan position of the probe and each channel position (in other words, the position on the substrate, of a detection point corresponding to each combination of exciting and detecting coils, and in JP-2008-8806-A, the position in the direction orthogonal to the probe scanning direction) on the substrate are taken as coordinates. Results of detection of the respective channels are also displayed in color tones of pixels of their corresponding coordinates. With such a display of flaw detection results, it is possible to determine the presence or absence of a flaw and evaluate the position and length of the flaw.
Incidentally, objects to be inspected by the eddy current flaw detection system have been expanded up to those each having an inspection surface of a complicate three-dimensional shape, like, for example, a weld between a reactor pressure vessel (RPV) and a stub tube of a control Rod Drive (CRD) (refer to, for example, JP-2008-298478-A (refer to FIGS. 20 and 21, etc.)).